Psoriasis is among the dermatoses having a poorly understood etiology. The ailment is a chronic skin disease usually occurring in early to middle age and affecting approximately 2% of the US population. Psoriasis is characterized by epidermal hyperplasia and a greatly accelerated rate of epidermal turnover. The lesions are characteristically dry, well demarcated, red, slightly raised and scaly. Gentle scraping of the lesion removes scales and produces many pinpoint bleeding sites, the so-called "Auspitz sign". The lesions are discrete or confluent erythromatous plaques and papules covered with white or silvery scales found on the extensor surfaces such as the elbows, knees, back and scalp. No part of the body is exempt. The lesions may be localized or generalized.
The therapies of choice are generally limited to the topical application of fluorinated corticosteriods, keratolytics containing salicylates, coal tar, anthralin preparations and systemic therapy with corticosteroids and methotrexate. Methotrexate and drugs like it have severe side effects such as bone marrow depression and thus their therapeutic benefits must be weighed against potentially dangerous side effects. In addition, the formulations to be used are limited to the most common preparations such as, solutions, creams, and salves. Consequently, the manner of application for the dermatherapy is practically predetermined.
Typically the only pharmaceutical forms in which the therapeutic agents are available are lipophilic preparations for local therapy, due to the high instability of the active ingredients against air, oxygen, water, and alkalis. The strongly fattening lipophilic preparations have relatively low storage stability. Such preparations are necessarily inconvenient to use because the hydrophobic preparations are difficult to wash off.
A hydrophilic pharmaceutical preparation capable of delivering a therapeutic agent for the treatment of psoriasis is needed. The preparation would also need to have a high storage stability, and be innocuous, and non irritating to the skin. A therapeutic agent that is nontoxic and effective in treating psoriasis is also needed.